It is now well-established that in the early-stage of human immunodeficiency virus (HIV) infection and throughout the clinical latent stage, viral particles accumulate and replicate actively in lymphoid organs despite a low viral load in peripheral blood. The high viral load observed in the lymphoid tissues was reported to be partly associated with trapped HIV particles on the follicular dendritic cells (FDC) located in the germinal centers. In addition to the extracellular localization of HIV in interdendritic spaces of germinal centers, viral particles are also found within the endosomal and cytoplasm compartments of FDC. Moreover, viral particles bound to the FDC remained highly infectious to CD4+ T-cells despite the presence of neutralizing antibodies on their surface. Over the course of HIV infection, the FDC network was shown to be gradually disrupted and ultimately destroyed. The incapacity of FDC to retain HIV particles in advanced stages of the disease has been postulated to contribute to the increased viral burden in the periphery. As the microenvironment of lymphoid tissues is crucial for effective immune responses, it is important to reduce or abrogate the production and the accumulation of HIV-1 particles in these tissues to preserve both their architecture and integrity.
Highly active antiretroviral therapy (HAART), usually consisting in the combination of two nucleoside analogues and one protease inhibitor, has been shown to be effective to reduce the plasma viral load to undetectable levels in HIV-infected individuals. However, anti-HIV regimens do not fully eliminate viral replication in secondary lymphoid tissues and this continued replication of HIV-1 seems to be due to the presence of drug-sensitive viruses. In addition, replication-competent HIV-1 are routinely isolated from resting CD4+ T-cells from patients receiving HAART even after 30 months of therapy (Finzi et al., 1997, Science, 278:1295-1300). In fact, it was estimated that it would take as much as 60 years to eradicate HIV from an infected individual (Finzi et al., 1999, Nature Med. 5:609-611). In addition, it was shown that initiation of HAART in HIV-infected patients, as early as 10 days after the onset of symptoms of primary HIV-1 infection, did not prevent generation of latently infected resting CD4+ T-cells carrying integrated HIV-1 DNA despite the successful control of plasma viremia (Chun et al., 1998; Proc. Natl. Acad. Sci. USA 95:8869-8873). On the other hand, an increasing number of treatment failures resulting from toxicity, drug-resistant mutants and/or poor compliance of patients to drug regimen are emerging with long-term therapy.
All approved anti-HIV drugs are generally aimed at blocking viral replication within cells by inhibiting either HIV-1 reverse transcriptase or protease which are essential enzymes for viral replication. Antiviral drugs include anti-HIV drugs such as 3′-azido-3′-deoxythymidine (AZT, zidovudine), 2′-3′-dideoxyinosine (ddI; didanosine), 2′-3′-dideoxycytidine (ddC; zalcitabine), 2′-deoxy-3′-thiacytidine (3TC; lamivudine), indinavir, saquinavir, ritonavir, nelfinavir, ganciclovir, foscarnet and ribavirin. The development of new drugs that targets other events of HIV-1 infection or the use of alternative approaches for the treatment of HIV-1 infection remains a high priority to cure this deadly disease. Most polyene macrolide antibiotics are active against a variety of lipid-enveloped RNA and DNA viruses. The binding of these drugs to sterols located within microbial cell membranes modifies the permeability and function of cells decreasing the infectivity of lipid-enveloped virus. Both amphotericin B (AmB) and nystatin A have been shown to be efficient to inhibit the in vitro replication of HIV-1, probably via the binding of drugs to cholesterol in the membrane of HIV-1, which has a high cholesterol-to-phospholipid ratio. Antiviral activity of a series of more soluble derivatives of AmB has also been investigated. The mechanism of action by which these molecules inhibit HIV-1 infection was shown to be markedly different upon the nature of the AmB derivative, their main target being the viral and/or cellular membrane.
One common feature of retroviruses, as well as of many other enveloped viruses, is the acquisition of host cell surface molecules during the budding process. FDC, B lymphocytes, antigen presenting cells like macrophages and activated CD4+ T-cells are abundant in lymphoid tissues and all express substantial levels of the HLA-DR determinant of the major histocompatibility complex class II (MHC-II). Monocyte-derived macrophages, which are also CD4+ and express HLA-DR, are considered to be the most frequently identified hosts of HIV-1 in tissues of infected individuals. Given that HIV-1 has been reported to incorporate a vast array of cell membrane derived structures while budding out of the infected cell, the probability that newly formed viral entities will bear cellular HLA-DR is thus high. It has been demonstrated that plasma HIV-1 isolates from virally-infected individuals do carry on their surface host-encoded HLA-DR (Saarioos et al., 1997, J. Virol. 71:1640-1643). The physiological relevance of cellular HLA-DR bound to HIV-1 is further provided by previous studies from our laboratory indicating that HLA-DR is one of the most abundant host-derived molecules carried by HIV-1 (Cantin et al., 1997, J. Virol. 71:1922-1930). Numerous reports have provided evidence for the presence of many other host-derived components in different laboratory and/or primary isolates of HIV-1 (Table 1; for review see Tremblay et al., 1998, Immunol. Today 19:346-351).
There is serious doubt about the ability of current antiviral treatment to eradicate HIV-1 infection. Therefore, more potent antiretroviral drugs or the use of alternative approaches that block the potential spread of virus within lymphoid tissues, their main reservoir, are urgently needed. Considering that HIV accumulates and replicates actively within lymphoid tissues, any strategy that will decrease viral stores in these tissues might be beneficial to the infected host. As liposomes are naturally taken up by cells of the mononuclear phagocytic system (MPS), liposome-based therapy represents a convenient approach to improve the delivery of anti-HIV agents within lymphoid tissues. As host-derived HLA-DR proteins are abundantly expressed on antigen presenting cells such as monocyte/macrophages and FDC, liposomes bearing surface-attached anti-HLA-DR antibodies (anti-HLA-DR immunoliposomes) and containing anti-HIV agents constitute a convenient approach to target even more specifically HIV-1 reservoirs. Similarly, the coupling of anti-CD4 molecules on the surface of liposomes (anti-CD4 immunoliposomes) should lead to a specific targeting of both CD4 T-lymphocytes and monocyte/macrophages which represent the major cellular reservoir for HIV-1. Furthermore, as host-encoded HLA-DR determinant is also present on the virion's surface, incorporation of neutralizing agents, such as amphotericin B, in anti-HLA-DR immunoliposomes represents an attractive strategy to destroy cell-free viruses. Taken together, the use of immunoliposomal drugs represents an attractive strategy to target primary cellular reservoirs of HIV-1. Such a targeted drug delivery system could hopefully improve the treatment of HIV infection.
U.S. Pat. No. 5,773,027 discloses the use of antiviral agents encapsulated into liposomes for the treatment of viral diseases. However, this publication does not specifically teach liposomes bearing surface-attached antibodies comprising or not a drug capable of inhibiting replication or destroying both cell-free HIV virions and virally-infected cells. Such immunoliposomes could represent a novel therapeutic strategy to treat more efficiently this retroviral disease.
TABLE 1Host proteins acquired by HIV-1Host protein (otherStrain of HIV-1name)Producer cell (cellular origin)a(source)bCD3 (T3)H9 (T)IIIB (L)CD4 (T4)PBMCs, H9 (T)IIIB (L)CD5 (T1)PBMCs, H9 (T)IIIB (L)CD6 (T12)PBMCs, H9 (T)IIIB (L)CD8 (T8)Sup-T1 (T)IIIRF (L)CD11a (LFA-1)PBMCs, H9 (T), Sup-T1 (T),IIIB (L), IIIRF (L),CEMx174 (T), Jurkat (T),P1 (P)CEM.NKr (T), C8166 (T),U937 (M), AA2 (B)CD11b (Mac-1)H9 (T), U937 (M)IIIB (L)CD11c (gp 150,95)H9 (T), U937 (M), AA2 (B)IIIB (L)CD15 (Lewis-X)U937 (M)IIIB (L)CD18PBMCs, H9 (T), Sup-T1 (T),IIIRF (L), IIIB (L),Jurkat (T), CEMx174 (T),P1 (P)CEM.NKr (T), C8166 (T)U937 (M), AA2 (B)CD19AA2 (B)IIIB (L)CD25 (Tac)PBMCs, H9 (T)IIIB (L)CD30 (Ki-1)H9 (T)IIIB (L)CD43PBMCs, CEMx174 (T),IIIRF (L), IIIB (L)(leukosialin,Jurkat (T), CEM.NKr (T),sialophorin)Sup-T1 (T), H9 (T),U937 (M), AA2 (B)CD44 (Pgp-1)CEMx174 (T), Sup-T1 (T),IIIRF (L)CEM.NKr (T)CD48 (Blast-1)PBMCs, H9 (T), U937 (M)IIIB (L)CD54 (ICAM-1)PBMCs, H9 (T), C8166 (T),IIIB (L), IIIRF (L),U937 (M), AA2 (B),LAI (L), NL4-3 (L),RAJI-CD4 (B)P1(P), 334 (P),336 (P), 438 (P)CD55 (DAF)PBMCs, H9 (T), U937 (M),NL4-3 (L), IIIB (L),AA2 (B)JC50 (P),MG 47 (P),MP49 (P),PE51 (P), CJ48 (P)CD59 (Protectin,PBMCs, H9 (T), U937 (M),NL4-3 (L), IIIB (L),Mac inhibitor)AA2 (B)JC50 (P),MG 47 (P),MP49 (P),PE51 (P), CJ48 (P)CD63PBMCs, H9 (T), Jurkat (T),IIIB (L), IIIRF (L)Sup-T1 (T), CEMx174 (T),CEM.NKr (T)CD71 (TransferrinPBMCs, CEMx174 (T),IIIRF (L), IIIB (L)receptor)Sup-T1 (T), H9 (T),U937 (M), AA2 (B)CDw108 (GR2)H9 (T), U937 (M), AA2 (B)IIIB (L)Cyctophilin ACEMss (T), HeLa (E),NL4-3 (L),COS (F)HXB2 (L)HXBH10 (L),IIIMN (L)CytosketetalH9 clone 4 (T), CEMss (T)IIIMN (L)proteinsPBMCs, RAJI-CD4 (B)LAI (L), IIIRF (L),HLA-DP, -DQNL4-3 (L), 334 (P),336 (P), 438 (P)Abbreviations: HIV-1: human immunodeficiency virus type 1; HLA-DP and DQ, human leukocyte antigen loci DP and DQ; PBMCs, peripheral blood mononuclear cells.aCellular origin: B, B-lymphoblastic; E, epithelial-like; F, fibroblast-like; M, monocytic; T, T lymphoblastoid. bSource: L, laboratory isolates of HIV-1; P, primary isolates of HIV-1.